(1) Field of Invention
The present invention relates to an apparatus and method for protecting a conduit which may be a cable to be installed subsea and particularly but not exclusively relates to a method and apparatus for protecting a cable such as a Direct Electrical Heating (DEH) cable that is attached to fluid flowline (in a manner known in the art as “piggybacked”) that is to be installed subsea.
(2) Description of Related Art
Conventionally, fluid flowlines such as oil flowlines are arranged to transport oil from subsea wellheads and/or from offshore production platforms to oil and gas storage facilities and refineries onshore, and such flowlines are conventionally installed subsea in a reeled pipe lay operation from a flowline installation vessel such as a reel lay vessel such as the Seven Oceans operated by the present applicant Subsea 7.
In a lot of oil wells, the oil is relatively highly viscous and the viscosity increases the lower the temperature of the oil drops. Accordingly, it is conventional to heat the oil flowing through the flowlines in order to prevent the viscosity rising by using either induction heating or trace heating. In either case, electrical cables need to be run to provide the closed circuit required. In the induction heating case, the return cables are the DEH cables.
FIG. 4 shows a conventional prior art DEH cable 1 which is arranged to provide electrical power to wire heating elements (not shown) installed at two or more longitudinally spaced apart locations in the side wall of a conventional steel flowline 3. As can be seen in FIG. 3, the flowline 3 is provided with suitable rigid insulation 5 in a conventional manner.
When installing flowlines 3 and DEH cables 1 on the sea bed, it is important to provide a Mechanical Protection System (MPS) for them in order to protect them (and particularly the otherwise exposed DEH cable 1) from dropped objects, fishing nets, anchors etc. as such objects can do great harm to DEH cables 1 and flowlines 3 which may result in the need to replace the whole flowline 3.
One such conventional MPS 10 that is not in accordance with the present invention is shown in FIGS. 1 to 4, in which:
FIG. 1 is a cross sectional view of a cover section 14 being brought toward a gutter section 12 of the conventional MPS 10;
FIG. 2 is a perspective side view of a number of gutter sections 12 of the conventional MPS 10 in a stacked configuration for transportation and/or storage;
FIG. 3 is a perspective view of a number of cover sections 14 of the conventional MPS 10 in a stacked configuration for transportation and/or storage; and
FIG. 4 is a cross sectional end view of the conventional MPS 10 of FIG. 1 shown in its in use configuration piggybacked on a flowline 3 with a DEH cable 1 being located in the cylindrical throughbore of the MPS 10 and being protected thereby.
As best seen in FIG. 4, the conventional MPS 10 comprises a main body 12 in the form of a gutter section 12 and an upper cap 14 in the form of a cover section 14 and which are shown in more detail and in isolation in FIG. 1. The main body 12 and the upper cap 14 comprise a suitable key 13 and slot 15 which, when mated, realisably secure the upper cap 14 to the main body 12 such that the structure of the upper cap 14 and main body 12 when coupled provide a protective structure around a cylindrical through bore 11 which in use forms a protective cylindrical chamber 11 suitable for protecting the DEH 1.
As can be seen in FIG. 4, the DEH piggyback cable 1 is loosely installed inside the inner bore provided by the MPS 10, and can thus move freely inside the MPS 10 to accommodate flowline 3 thermal differential expansion and flexing of the two relative to each other that might occur during their installation and handling.
The conventional MPS 10 of FIGS. 1 to 4 is assembled as follows. The flowline 3 and its insulation 5 are pulled off the reel on the flowline installation vessel (not shown). An engineer 17 either manually picks up or with the use of a crane or the like lifts a main body 12 and rests it on top of the insulation 5 of the flowline 3. Each main body 12 is in the region of 2.6 meters or so long and can weigh in the region of 17 to 26 kg each.
The DEH cable 1 is then pulled off its own reel (not shown) by a suitable machine and is placed into the semi-circular lower through bore portion 19 of the main body 12 such that it rests therein and one length of upper cap 14 is manually picked up by the engineer 17 or can be lifted with a crane or the like and manipulated such that the key 13 is brought towards and is fitted into the slot 15 (it being shown in FIG. 1 as being brought toward). A metal band 16 is then manually applied around the outer surface of the upper cap 14 and the main body 12 and also the outer surface of the insulation 5 such that the metal banding 16 ensures that the MPS 10 is held securely against the flowline 3. The MPS 10 thereby provides a protective chamber within or in the form of its cylindrical throughbore 11 for the DEH cable 1.
However, such a conventional MPS 10 suffers from several disadvantages. For instance, the main body or gutter section 12 and also the upper cap or cover section 14 are typically 2.6 meters long. Therefore, for a typical 11 km length of flowline 3, 4230 gutter sections 12 and 4230 cover sections 14 would be required. These would typically be supplied to the flowline installation vessel on wooden pallets and typically 100 such pallets would be required and these would be supplied within 40 containers which would take up the available deck space on an installation vessel many times over. Accordingly, the flowline installation vessel would need to be supplied on a regular basis with for example 3 or 4 containers per supply run. Consequently, the transportation/supply costs are very expensive. Furthermore, such a conventional MPS 10 heavily relies on manual handling of 8460 gutter and cover sections in total for a typical 11 km length of flowline 3 and this therefore poses a significant safety risk to the engineers 17 involved. Furthermore, the assembly of the gutter 12 and cover 14 sections, particularly because of the manual assembly, is very time consuming.
It is an object of embodiments of the present invention to mitigate such disadvantages with the conventional MPS 10 but still provide a reliable and an assured protection system for a DEH cable 1.